Oil and gas wells commonly bypass significant productive formations that may be uneconomic to complete at the time the well was drilled. These formations may be relatively thin and low pressure so simply perforating the zone does not provide significant new production. However, lateral drilling into such thin, horizontal oil bearing formations can result in substantial new oil production. The lateral well should be drilled at an angle as close as possible to 90 degrees relative to the vertical well to ensure that the lateral drilling tools stay within the productive zone. This objective can be accomplished by feeding a flexible lance equipped with a compact rotary jet drill though a shoe incorporating a curved passage that deflects the drill at a high angle into the formation. This approach is referred to as zero-radius lateral drilling, since the angle is defined entirely within the wellbore, as opposed to drilling a curved hole in the formation.
Conventional mechanical drilling requires high thrust and torque to penetrate rock. Applying high torque and thrust though a tight radius curve is extremely difficult. A rotary jet drill of the type described in U.S. Pat. No. 7,198,456 provides the ability to penetrate a range of underground formations with very low thrust load and no torque. The rotary jet drill includes a reaction-turbine jet rotor that spins a pair of forward facing jets that erode the formation. The jet drill face has a gage ring which, provided that the drill is kept pressed against the rock face, ensures drilling of a close tolerance circular section borehole.
It would be desirable to provide improved method and apparatus for zero-radius lateral drilling, for example, by using the rotary jet drill in a system that can apply the required torque and thrust through the tight curve defined within a borehole.